For an oil pan applied to a lubricating device for lubricating a lubricated object such as an engine and an automatic transmission with lubricating oil (hereinafter merely called oil), a so-called double-tank type oil pan is well-known. The double-tank type oil pan is provided with a first chamber that communicates with the lubricated object by being opened toward the lubricated object, a second chamber that is adjacent to the first chamber and communicates with the first chamber via an oil communicating channel and a partition provided between the first chamber and the second chamber.
For related art of this type of double-tank type oil pan, a double-tank type oil pan disclosed in JP-A No. 222012/2003 can be given.
This conventional type oil pan is provided with an oil pan separator having a concave part for forming the almost whole of the volume of a first chamber (or a main chamber) inside and the inside of the oil pan is vertically partitioned into the first chamber formed by the concave part and a second chamber (or a deputy chamber) outside the first chamber by the oil pan separator. The second chamber is formed substantially overall the sides and the bottom of the first chamber (or the concave part) by providing predetermined clearance between a lower surface at the bottom of the oil pan separator and the bottom of the oil pan. In the first chamber, a strainer is arranged which is provided with an oil suction opening open to the vicinity of an inner surface of the bottom of the first chamber and connected to an oil pump for delivering oil to a lubricated object via an oil channel.
A communicating hole as the oil communicating channel which can be regulated a degree of the communication of oil between the first chamber and the second chamber according to the temperature of the oil is formed in a lower part of the side of the concave part of the oil pan separator or slightly on the upside of the bottom panel of the oil pan. That is, a diameter of the communicating hole is set to a small value of approximately 2 mm so that high temperature oil having low viscosity can easily pass though low temperature oil having high viscosity cannot easily pass.
Functions of the communicating hole are as follows. First, the viscosity of oil is high at the time before warming up is finished in cold operation (hereinafter referred as “in cold starting”). Consequently, the communication of oil between the first chamber and the second chamber via the communicating hole is limited. Accordingly, in warming up, oil is supplied from the first chamber to the lubricated object, the lubricated object is lubricated, the oil the temperature of which rises by taking heat from the lubricated object in lubrication drops into the first chamber, is collected in the first chamber, is supplied to the lubricated object again, while an inflow of low temperature oil in the second chamber into the first chamber is limited. In other words, as in warming up, only oil in the first chamber can be supplied to the lubricated object, the heat capacity (the product of specific heat and mass) of oil that can be supplied to the lubricated object is small (in other words, the whole substantial heat capacity of oil pan structure including each component of the oil pan and oil is small). Therefore, the temperature of oil to be supplied to the lubricated object is easily raised and hereby, the warming-up time of the lubricated object is reduced.
Afterward, when warming up proceeds and the temperature of oil in the first chamber rises, the temperature of oil in the second chamber also gradually rises because heat is transmitted to the oil in the second chamber via the oil pan separator. When the viscosity of the oil in the second chamber in the vicinity of the communicating hole becomes low to the extent that the oil can easily pass the communicating hole, the sufficient communication of oil between the first chamber and the second chamber via the communicating hole is enabled. In this case, the oil flows from the second chamber into the first chamber through the communicating hole by negative pressure caused in the vicinity of an oil suction opening of the strainer, and the oil flowing in from the second chamber can be supplied to the lubricated object. Hereby, as the almost whole oil inside the oil pan can be supplied to the lubricated object, the lubricated object can be satisfactorily lubricated and the heat capacity of oil that can be supplied to the lubricated object increases (in other words, the whole substantial heat capacity of the oil pan structure including each component of the oil pan and oil increases). Therefore, the excessive temperature rise of the lubricated object can be restrained.
Further, a drain hole for outpouring oil from the first chamber to the second chamber when oil is to be removed from the inside of the oil pan is formed at a lowest position of the bottom panel of the oil pan separator in addition to the communicating hole. A drain plug hole for removing oil is provided to the oil pan and oil in the second chamber which is an outermost area of the oil pan is discharged outside the oil pan by pulling out a drain plug that closes the drain plug hole and releasing the drain plug hole. Oil in the first chamber which is an inner area once flows out into the second chamber through the drain hole and then discharged outside the oil pan. In the meantime, as described above, the drain hole is formed in the lowest position of the bottom panel of the oil pan separator, in other words, in the lowest position in the first chamber. The oil suction opening of the strainer is also arranged close to the inner surface of the bottom of the first chamber as described above. Accordingly, when oil in the first chamber is sucked by the strainer in warming up, there is a concern about flowing low temperature oil in the second chamber into the first chamber through the drain hole by negative pressure caused by the strainer and diminishing the effect of the reduction of warming-up time. Accordingly, though the fact described below is not definitely described in JP-A No. 222012/2003, a diameter of the drain hole is required to be formed in size in which low temperature oil in the second chamber in warming up cannot easily pass, that is, in the similar size to the communicating hole.